There is known a plasma processing apparatus for processing an object by using a plasma of a processing gas. For example, Japanese Patent Application Publication No. 2004-511906 discloses a capacitively coupled plasma processing apparatus including a processing chamber, a mounting table and an upper electrode. The mounting table is provided at a lower portion of the processing chamber. The mounting table mounts thereon an object to be processed and serves as a lower electrode. Further, the mounting table includes an edge ring surrounding an outer periphery of an electrostatic chuck for attracting and holding the object. The upper electrode has a central portion and a peripheral portion. The upper electrode is provided at an upper portion of the processing chamber.
In the apparatus disclosed in Japanese Patent Application Publication No. 2004-511906, the upper electrode has a stepped portion having a trapezoidal cross section and protruding downward from a surface of the upper electrode which faces a processing space. The stepped portion is formed at a peripheral portion of the upper electrode so as to face the edge ring of the lower electrode. Since the apparatus disclosed in Japanese Patent Application Publication No. 2004-511906 has such a stepped portion, a plasma density in a region near the peripheral portion of the upper electrode is locally increased, thereby increasing the etching speed at a peripheral region of the object.
When a semiconductor device is manufactured, it is required to reduce dimensional variation of a shape formed at the entire area of the object. In the apparatus disclosed in Japanese Patent Application Publication No. 2004-511906, the etching speed near the peripheral portion of the upper electrode can be controlled by the stepped portion formed at the upper electrode. However, an etching speed at an outermost peripheral region of the object may not be sufficiently increased depending on processing gases. In that case, a shape formed at the central region of the object may be different from a shape formed at the outermost peripheral region of the object. The present inventors have studied on the above problem and found that a plasma density in a space above an outside of the outer periphery of the mounting table needs to be controlled in order to control the dimension of the shape at the outermost peripheral region of the object.